This invention relates to a solid-state imaging device and a method of driving the same, and more particularly to a solid state imaging device capable of independently and simultaneously reading out all pixel signals and a method of driving such an imaging device which is used in broadcasting CCDs, high-picture quality civil use CCDs, electronic cameras, etc.
As a CCD area sensor capable of providing a high resolution of the solid state imaging devices using a charge transfer device, there is known a CCD area sensor in which photosensitive elements producing signal charges of two pixels constituting one line are arranged adjacently to each other in a column direction (vertical direction). However, in CCD area sensors generally used as the area sensor for civil use, from a view point of the requirement of miniaturization, in order to reduce the number of transfer stages requiring a broad area, a readout system is employed to add signal charges of two pixels adjacent in a column direction to read out the added one, with the result that signals outputted from the area sensor have a lowered resolution with respect to the column direction.
From the viewpoint of recent requirements of the high picture quality and the high resolution, there have been proposed various techniques ,-as to the all pixel signal independent readout to simultaneously and independently read out all pixel signals without carrying out addition.
FIG. 1 is a plan view showing the outline of the configuration of a conventional solid state imaging device capable of simultaneously and independently reading out all pixel signals. For brevity of explanation, a solid-state imaging device in which the number of pixels is reduced will be described, but it should be noted that actual solid state imaging devices have exactly the same structure and perform the same operation except that actual solid state imaging devices have a larger number of pixels.
In this solid state pickup device, photosensitive elements 1 to 8 belonging to the first to the eighth rows constitute each photosensitive element train 10 in a row, and a column transfer section 20 is formed adjacently to each photosensitive element train 10. Each column transfer device 20 is such that one transfer stage is formed with respect to two photosensitive elements, and that it comprises transfer stages 11 to 14. In this example, there are formed sets of the photosensitive pixel trains 10 and the column transfer sections 20 corresponding to five columns.
At the lower portion of the column transfer section 20, a charge storage section 30 comprised of four transfer stages 21 to 24 are formed. There is employed an arrangement such that two columns of charge storage subsections 31 and 32 correspond to one column transfer section 20. Thus, signal charges transferred by the column transfer section 20 will be interchangeably transferred to the two columns of charge storage subsections 31 and 32.
Further, at the lower portion of the charge storage section 30, two rows of row direction transfer sections 33 and 34 including five transfer stages are formed, and output circuits 35 and 36 are connected to the final transfer stages, respectively. These row direction transfer sections 33 and 34 serve to receive signal charges transferred by the charge storage sections 31 and 32 to transfer them in directions of the output circuits 35 and 36, respectively. These output circuits serve to take out voltage signals from signal charges.
The procedure for concurrently reading out all pixel signals in such a conventional solid-state imaging device will now be described. It should be noted that signal charges produced from photosensitive elements 1 to 8 are respectively represented by reference symbols S1 to S8 in the following description.
First, signal charges S1, S3, S5 and S7 stored in the photosensitive elements 1, 3, 5 and 6 belonging to the odd row are respectively transferred to the transfer stages 14, 13, 12 and 11 to transfer these signal charges in a column direction by driving the column transfer section 20 to allow the charge storage subsection 31 to store them thereinto. It is now assumed that signal charges in the state where they are stored in the charge storage section 30 are represented by corresponding reference symbols with prime. Then, signal charges S2, S4, S6 and S8 belonging to the even rows are respectively transferred to the stages 14, 13, 12 and 11 of the column transfer section 20 to transfer these signal charges in a column direction to allow the charge storage subsection 32 pairing with the charge storage subsection 31 used in the last transfer to store them thereinto. Then, the respective five signal charges S1' and S2' stored in the transfer stage 24 of the lowermost stage of the charge storage section 30 are transferred in parallel to corresponding transfer stages of the row direction transfer sections at predetermined timings. Namely, five signal charges S1' in the charge storage subsection 31 are transferred to the row direction transfer section 34 via the row direction transfer section 33, and signal charges S2' in the charge storage, subsection 32 are transferred to the row direction transfer section 33 at the same timing as the timing at which the signal charge S1' is transferred from the row direction transfer section 33 to the row direction transfer section 34. The signal charges S1' and S2' transferred to these row direction transfer sections 33 and 34 are sequentially outputted at the same timing.
At a predetermined time after the signal charges S1' and S2' are all outputted, signal charges S3' and S4' in the charge storage section 30 are transferred to the row direction transfer sections 33 and 34 in accordance with a procedure similar to the above, and are outputted therefrom, respectively. It is to be noted that since image information shared by respective signal charges are prescribed by the time at which they are transferred from the photosensitive pixels to the first column transfer section, there would occur disagreement between image information of the odd row and that of the even row. However, by allowing the column transfer to be carried out at a high speed, such a disagreement can be held down to such an extent that there is no problem from a viewpoint of practical use.
At times subsequent thereto, by repeatedly performing such an operation, it is possible to read out signals from the all photosensitive pixels. The reason why the system of simultaneously reading out two rows is employed, is to cope with the interlacing operation in the ordinary television system.
As described above, in the prior art, it is required to transfer, via one row direction transfer section, one of even row charges and odd row charges to another row direction transfer section remote therefrom. To realize this, it is necessary to independently control signal charges produced at the photosensitive elements of the odd rows and signal charges produced at photosensitive elements of the even rows to transfer them. This results in the problems that the structure of the transfer section is complicated, and that transfer control of charges becomes complicated because transfer between row direction transfer sections must be carried out.